Transient Enhancement and Detuning of Laser-Driven Parametric Instabilities by Particle Trapping

Vu, H. X.; DuBois, D. F.; Bezzerides, B.

doi:10.1103/physrevlett.86.4306

Cited by 136 publications

(121 citation statements)

References 19 publications

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“…3, the saturation of instability due to the detuning as predicted in Ref. 3 was not observed in optical mixing. This is because there is a corresponding shift for wavevectors ͑as can be seen for instance in Fig.…”

Section: Homogeneous Slab Density Profilementioning

confidence: 55%

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Saturation process induced by vortex-merging in numerical Vlasov-Maxwell experiments of stimulated Raman backscattering

et al. 2007

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The influence of low-frequency nonlinear Bernstein-Greene-Kruskal ͑BGK͒-type waves induced by trapped electrons in backward stimulated Raman scattering is investigated in optical mixing. Semi-Lagrangian Vlasov-Maxwell simulations show two nonlinear behaviors. First, there is a Morales-O'Neil plasma wave frequency downshift retuned by a small wavenumber shift which maintains the Stimulated Raman Scattering ͑SRS͒ resonance. The saturation of Raman backscattering begins with phase space vortex merging followed by a transition to lower wavenumbers following the ͑nonlinear͒ dispersion relation, resembling weak turbulence.

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Section: Homogeneous Slab Density Profilementioning

confidence: 55%

“…Vu et al in Ref. 3 propose a saturation of SRS by detuning due to the nonlinear frequency shift of the EPW, while Brunner and Valeo in Ref. 4 have suggested the breakup of EPW through the trapped-particle instability.…”

Section: Introductionmentioning

confidence: 99%

Saturation process induced by vortex-merging in numerical Vlasov-Maxwell experiments of stimulated Raman backscattering

et al. 2007

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“…For example, detailed inspection of the data which generated figure 8 shows that the maximum, κ norm srs ( ) max , is at kλ D =0.465, eφ/T e = 0.042 with a value of 0.072, which corresponds to the point on the solid curve in figure 9 at n e / n c = 0. Although there is no possibility of resonance, the departure from resonance is soft compared to the decrease of damping for small φ at 0.08n c , so that the optimum value of φ is finite and the gain rate is nearly twice the linear value 31 . The optimum value of φ is shown in figure 11.…”

Section: Examples Of Bsrs Maximum Gain Rate For Nif and Nova Relementioning

confidence: 99%

Trapped particle bounds on stimulated scatter in the large kλD regime

Rose

2003

Physics of Plasmas

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In the strongly damped regime, the convective gain rate for stimulated scatter, κ, is customarily maximized by requiring that, taken together, the laser light wave and the daughter light and plasma waves, satisfy wavevector and frequency matching, and then 1/κ~γ, the plasma wave damping rate. If the bounce frequency in the daughter plasma wave is large compared to the trapped particle loss rate, it would seem, based on naïve , and asymptotes to a finite value for large φ, when the loss of * har@lanl.gov 2 trapped electrons due to convection out the speckle sides dominates that due to collisions.This behavior, combined with the loss of resonance for φ too large, leads to a maximum value for κ as a function of scattered light frequency and φ, for given laser and plasma parameters. Bounds for stimulated Brillouin scatter gain rate are also obtained. The standard mode-coupling model (MCM) of these scattering processes, when modified to include the trapped particle nonlinear frequency shift, always allows for a propagating plasma wave, and therefore may be qualitatively in error in regimes where the daughter plasma wave loses resonance. A mean field approximation model is proposed which is consistent with the bound on κ and agrees with the MCM in the resonant regime, but differs in the non-resonant regime by respecting this fundamental difference in the plasma mode structure. If a plasma, as it evolves, crosses the resonant/non-resonant regime boundary, a model that is cognizant of both regimes is required to avoid a qualitative overestimate of the scatter.

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“…However, recent experiments [4][5][6] and kinetic simulations [7][8][9][10][11][12] have shown SRBS reflectivities well above coupled-mode convective gain levels. * Electronic address: dstrozzi@llnl.gov This kinetic inflation or enhancement of SRBS is widely attributed to electron trapping in the EPW potential well, which flattens the electron distribution function near the EPW phase velocity v p2 [7,13]. As has long been known, trapping reduces the EPW damping rate [14] and induces an amplitude-dependent frequency downshift [15].…”

Section: Introductionmentioning

confidence: 99%

Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter

et al. 2007

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1-D Eulerian Vlasov-Maxwell simulations are presented which show kinetic enhancement of stimulated Raman backscatter (SRBS) due to electron trapping in regimes of heavy linear Landau damping. The conventional Raman Langmuir wave is transformed into a set of beam acoustic modes [L. Yin et al., Phys. Rev. E 73, 025401 (2006)]. For the first time, a low phase velocity electron acoustic wave (EAW) is seen developing from the self-consistent Raman physics. Backscatter of the pump laser off the EAW fluctuations is reported and referred to as electron acoustic Thomson scatter. This light is similar in wavelength to, although much lower in amplitude than, the reflected light between the pump and SRBS wavelengths observed in single hot spot experiments, and previously interpreted as stimulated electron acoustic scatter [D. S. Montgomery et al., Phys. Rev. Lett. 87, 155001 (2001)]. The EAW observed in our simulations is strongest well below the phase-matched frequency for electron acoustic scatter, and therefore the EAW is not produced by it. The beating of different beam acoustic modes is proposed as the EAW excitation mechanism, and is called beam acoustic decay. Supporting evidence for this process, including bispectral analysis, is presented. The linear electrostatic modes, found by projecting the numerical distribution function onto a GaussHermite basis, include beam acoustic modes (some of which are unstable even without parametric coupling to light waves) and a strongly-damped EAW similar to the observed one. This linear EAW results from non-Maxwellian features in the electron distribution, rather than nonlinearity due to electron trapping.

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Transient Enhancement and Detuning of Laser-Driven Parametric Instabilities by Particle Trapping

Cited by 136 publications

References 19 publications

Saturation process induced by vortex-merging in numerical Vlasov-Maxwell experiments of stimulated Raman backscattering

Saturation process induced by vortex-merging in numerical Vlasov-Maxwell experiments of stimulated Raman backscattering

Trapped particle bounds on stimulated scatter in the large kλD regime

Kinetic enhancement of Raman backscatter, and electron acoustic Thomson scatter

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